How sharp is sharp?

HeavyHanded said:
This ^

Becoming more proficient with finer hones and having a handful to work with and push yourself to improve, will make all your edges better quality. The margin of error shrinks as the abrasive becomes smaller, so it pushes your technique.

It won't make the edge perform any better from an EDU perspective unless your normal use is carving, chopping or shaving.
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I'm working on it!! Being retired now make it easier to spend time on this!
 
Cutting newsprint is usually a pretty good test of sharpness. A knife that will cut newsprint easily with a slicing motion, along the entire length of the blade, has been properly apexed and de-burred. I keep a phone book on the bench and pull out pages as I need them. Even my Coarse DMT, with the right touch, can get a knife slicing through newsprint very easily. If it hangs up anywhere, that means you either have a burr or don't have a clean apex.

BTW, a knife with a burr will shave hair, sometimes impressively well, but the moment you try to cut anything else, the burr folds over and the knife acts dull. The newsprint method will let you know the truth real fast.
 
A edge, on any edged tool, shall only be as sharp as it need to be for its purpouse. Not sharper then that - in my opinion.

If you are in a competition about the sharpest edge possible - the edge shall be as sharp as possible.

If you sharpen your hunting knife to razor knife sharpness - you have change your hunting knife purpuse to a razor knife. You cannot use it as a hunting knife any more. It is to sharp.

The small U shape on the edge close to the handle can kill you. If you shall cut your self free from a fishing net in cold water, the fishing ner strings fasten in that U all the time - and time is just what you dont have in that situation...

An edge, in my mind and experiance, shall only be as sharp it need to be for its purpouse - and the sharpness must allways be in balance with needed retention - that balance makes that you also can use your knife long time before you must sharpen it again.

If your knife are to sharp for its purpouse - it will be dull fast...

Thomas
 
I like cutting the cellophane from cigarette boxes.
At work, i can tell by touching how sharp my edge is.
Long ago I used to roll a sheet of wax/parchment paper into a pencil thickness tube, and wrap it with many layer of plastic food wrap. Lay it on the cutting board and make 1 slice, if it can't cut trough I'll restart whole process.
for my line of work, i remove as much shoulder as possible, since the edge barely makes slicing contact and almost never any direct chopping contact, I can sacrifice material behind the edge.
I like to cut wax paper to the point there's almost no noise. Makes me happy.
 
EdgePal said:
A edge, on any edged tool, shall only be as sharp as it need to be for its purpouse. Not sharper then that - in my opinion.

If you are in a competition about the sharpest edge possible - the edge shall be as sharp as possible.

If you sharpen your hunting knife to razor knife sharpness - you have change your hunting knife purpuse to a razor knife. You cannot use it as a hunting knife any more. It is to sharp.

The small U shape on the edge close to the handle can kill you. If you shall cut your self free from a fishing net in cold water, the fishing ner strings fasten in that U all the time - and time is just what you dont have in that situation...

An edge, in my mind and experiance, shall only be as sharp it need to be for its purpouse - and the sharpness must allways be in balance with needed retention - that balance makes that you also can use your knife long time before you must sharpen it again.

If your knife are to sharp for its purpouse - it will be dull fast...

Thomas
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This is good advice.

As a second quick index I subscribe to one of Murray Carter's definitions - "three finger sticky and shaves arm hair". Like Trouthound, I get a lot of info from making different cuts on thin paper.
 
I've learned that not all knives benefit from razor sharp edges. I have sharpened some of my thicker tactical knives to a razor sharpness, and found out it wont cut well, and kept sharpening it until the edge became soo thin, the knife wasn't ideal for tactical purpose no more (kept shaving too much steel at a certain degree)

I use normal methods to see how sharp my edges are... from cutting paper to cardboards (push cut, slice, feather cuts etc.). But I can tell that it's pretty darn sharp by gently running a finger across the edge. Even a slight rub feels like the edge is sinking into/gripping my skin to where if I go any further, I'll get cut. I seen a friend get a decent cut when he ran his finger on one of my knives that I just sharpened. I guess he wasn't use to such sharp edge, and ran his finger across the edge the way he normally do for his duller knives. He didn't even apply much pressure l, but it was sharp enough to cut him before he can react to that cut feeling you get when edge penatrate your skin.
 
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TripleF100 said:
Maybe this sounds stupid! I admit I'm fairly new to this forum and I'm a complete failure at freehand sharpening. I use my Sharpmaker exclusively and it seems to do . . . well . . . okay. I do strop with green compound.

Recently, I decided to spend a lot of time on one knife and try and get it REALLY sharp. I keep hearing about a mirror polished edge and see plenty of pictures of the work some of you guys do. I was never able to achieve that degree of smoothness but I did get my knife pretty sharp!

But here is the deal . . . cutting stuff in my normal, everyday life I believe my knife actually cuts better if the edge is a little more ragged. Does this make sense??

Would spending the time (and money in my case!) to achieve that mirror edge make my knife sharper? Make it really cut better?
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It absolutely does make sense, and it is an oft-discussed topic here. For many EDC cutting tasks, many people find a "toothier" edge to be the best choice.

As for whether or not spending the time to achieve a mirror edge would make your knife sharper, technically yes, it would. But what it really does it make the edge more refined, and no, it won't necessarily make it cut "better" because that would depend on the cutting task at hand. A good example would be cutting a tomato. You'll probably appreciate a nice "toothy" edge for slicing tomatoes over a very refined mirror edge.
 
There is a difference between sharp and thin.
An axe can be screaming sharp but still chop properly if the edge angle isn't to small.
 
The sharper the better.

A good clean apex is sharp at any geometry.

Its the geometry that is task specific.
 
Bobby3326 said:
Please divulge how a sharp polished knife could get anyone killed from cutting any material.
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A fair question...

When saying this I mostly think of this story I read in the late 80s, or thereabout, when fully serrated one-hand opening knives with pocket clip, which at the time still meant mostly Spydercos, were a fairly new concept.

The man that was quoted in the magazine was directly relevant the article, so it seemed to me the magazine fully endorsed the story as credible: He worked in a factory and described how his jacket got caught into some heavy machinery, and started to pull him into its maws...: He got out the Spyderco, a fairly small one, I think a Delica, maybe an Endura at most, and cut up his jacket enough to tear himself out of it...

He stated: "If not for the Spyderco I would be dead: Everything else would have been too slow."

I have to extrapolate here what a rough grit edge would have done compared to a serrated edge, but a rough grit edge would have given you a far better chance than one of those mirror polished edges... That is what I meant by getting you killed...

Also, better slicing performance means you use less force, and too much force can cause you injury far away from help. I know from a particular ambulance ride that extra cutting effort can catch you in complicated ways you can't begin to imagine...

I sometimes finish up with a medium stone when there is a tenacious wire edge, but I am usually quite happy to leave the grit finish from my slightly worn Coarse Dia-sharp hone as the final finish, from a start in Extra-Coarse, always thinking about that jacket... And my ambulance ride... And don't bring a dull knife to "save" on a good one, however well mirror-polished...

Gaston
 
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DeadboxHero said:
The sharper the better.

A good clean apex is sharp at any geometry.

Its the geometry that is task specific.
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Yes and no.

Geometry is macro, edge finish is micro.

The same geometry prep'd a variety of finishes will create notable differences in performance depending on material to be cut and mechanism (draw, press). Geometry changes will maximize this performance up to the point where stability falls off. Both factors are influenced by steel type and RC.
 
Alright I have to know,

Why do high vanadium steels work better with a coarse finish?

Whats the mechanism involved?
 
DeadboxHero said:
Alright I have to know,

Why do high vanadium steels work better with a coarse finish?

Whats the mechanism involved?
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I don't really buy it, myself. To me, there's nothing unique about high-V steels that requires a coarser finish in order to 'work better' (whatever that means). It's definitely EASIER to 'make it work' at a coarser finish, as it doesn't require the same time or attention to detail as going further in finish without rounding it off. If the edge is finished with the abrasives best-suited to such steels (diamond, CBN), and with good technique and care, the carbides can still be shaped crisply at the edge, and the supporting steel matrix needn't be eroded away around them (which could happen if using abrasives which aren't up to shaping & cutting the carbides, and instead only dig away at the supporting matrix steel, thereby allowing the carbides to chip out).

Many will claim the same for D2, saying it works 'better' with a toothy edge. But I've always liked how it holds up with a more polished edge (2K+), so long as it's done carefully. Good steel is good steel, and the better ones will do well with whatever finish you give them.

I think whether a particular finish 'works better' is much more dependant on what's being cut with it, rather than on the steel type itself.


David
 
Obsessed with Edges said:
I don't really buy it, myself. To me, there's nothing unique about high-V steels that requires a coarser finish in order to 'work better' (whatever that means). It's definitely EASIER to 'make it work' at a coarser finish, as it doesn't require the same time or attention to detail as going further in finish without rounding it off. If the edge is finished with the abrasives best-suited to such steels (diamond, CBN), and with good technique and care, the carbides can still be shaped crisply at the edge, and the supporting steel matrix needn't be eroded away around them (which could happen if using abrasives which aren't up to shaping & cutting the carbides, and instead only dig away at the supporting matrix steel, thereby allowing the carbides to chip out).

Many will claim the same for D2, saying it works 'better' with a toothy edge. But I've always liked how it holds up with a more polished edge (2K+), so long as it's done carefully. Good steel is good steel, and the better ones will do well with whatever finish you give them.

I think whether a particular finish 'works better' is much more dependant on what's being cut with it, rather than on the steel type itself.


David
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I see. Thanks man.
 
DeadboxHero said:
Alright I have to know,

Why do high vanadium steels work better with a coarse finish?

Whats the mechanism involved?
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I have no solid idea on this. Ankerson's testing seems to show a clear correlation between (all else being equal) a rougher finish on super steels and edge longevity cutting Manila. This does not mean they cannot be taken to a bright finish and still give good performance, just that they seem to run far longer when started at a lower finish. It is also far easier to reliably achieve.

For D2 with the larger carbides, I find the RC plays a huge role (as it seems to with most steels, but especially D2). My Eskabar just doesn't run for long at higher polish, while my BCMW D2 takes a screaming edge at brighter finish.
 
HeavyHanded said:
I have no solid idea on this. Ankerson's testing seems to show a clear correlation between (all else being equal) a rougher finish on super steels and edge longevity cutting Manila. This does not mean they cannot be taken to a bright finish and still give good performance, just that they seem to run far longer when started at a lower finish. It is also far easier to reliably achieve.

For D2 with the larger carbides, I find the RC plays a huge role (as it seems to with most steels, but especially D2). My Eskabar just doesn't run for long at higher polish, while my BCMW D2 takes a screaming edge at brighter finish.
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Would be cool to know how exactly you sharpen your D2 Eskabar since I got one too.
 
OP, relative to your sharpmaker, you're not using it to sharpen your knife as much as it is able to. Heavy Handed alludes to geometry and geometry is a major factor I learned to being sharp. Given two knives with the same perfect, clean, fully apexed edges, the one with the more obtuse bevel angle will be less sharp than the one with the more acute angle.

All other things being equal, a more acute, smaller bevel angle will be "sharper" than a more obtuse angle. On your sharpmaker, the 30 degree side is more acute. Therefore, to get your knife as sharp as possible with the sharpmaker, the knife must be profiled to match the 30 degree side. The 40 degree side is to put a micro bevel after you have profiled to the 30 degree side. At least, that's what sharpmaker says. The way I see it, is you can sharpen your knife to the 30 degree. Then when it gets dull and you need to sharpen it fast or you don't have the time to resharpen to the 30 degree side, you can use the 40 degree side. This way, you have a nice clean apexed edge while still having the sharper bevel angle of 30 degrees behind your edge.
 
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